Devices which can be rotated about an axis of rotation to drive liquid flows within the device are known as centrifugal liquid handling devices. Typically, it is necessary to control liquid flows in such devices in a way that allows flows to be started and stopped differentially in different parts of the device. In other words, often such devices require a liquid flow control unit (also referred to as a “valve”) to control the flow of liquid, in particular to start liquid flow out of an upstream chamber at a desired point in time. Arrangements for valves in centrifugal liquid handling devices include sacrificial valves, capillary valves and capillary siphon valves.
Sacrificial valves have the drawback of requiring some sort of interaction with the device from outside in order to open (“sacrifice”) the valve. While capillary valves and capillary siphon valves can be “opened” by controlling the speed of rotation of the device, they rely on surface tension effects to, respectively, retain liquid behind a surface tension barrier or draw liquid into a siphon conduit by capillary action. These valves therefore require careful choice of the material of the device in the region of the valve. What is more, they require a limited specific speed range for the device in order to operate the valve. Specifically, a capillary valve can remain “closed” only below a certain speed of rotation at which the surface tension barrier is overcome, and capillary siphon valves require the device to be slowed down sufficiently so that the capillary force can draw liquid into the siphon conduit.